Integrating Fine-Scale Habitat Mapping and Pore Water Analysis in Cold Seep Research: A Case Study from the SW Barents Sea

Seafloor exploration using geo-referenced imagery from towed camera systems permits the investigation of small-scale (sub-cm) seabed features and a better understanding of submarine biogeochemical and physical processes, environments and their linkages. Decades of visual exploration of cold seeps have uncovered a variety of chemosynthetic communities often associated with gas bubbling and methane-derived authigenic carbonates, with the spatial distribution of these features reflecting the magnitude of methane flux through the sediment. In this study, the benefits of an integrated approach based on site-specific seafloor imaging and pore water analysis are demonstrated in quantifying total methane fluxes associated with different seep-habitats. This includes the investigation of a newly discovered cold seep in the SW Barents Sea, identified as the Leirdjupet Fault Complex (73.5° N, 21° E, 300-350 m water depth), using a total of 18 km of TowCam dives and four multicore sediment samples. The results document an extreme variability in methane flux linked to seafloor habitats with estimated total fluxes of 136.2 g CH4 yr-1 from an area characterized by microbial mats and tubeworms (85 m2) and 87.8 g CH4 yr-1 from a methane-derived authigenic carbonate area (50 m2). Further integrated studies, at both habitat- and regional-scales, are required for monitoring cold seep evolution at high-latitude continental margins. These include the investigation of sites where the contemporaneous ice-sheet retreat, coupled with ocean warming, could lead to enhanced seafloor methane emissions from deep hydrocarbon and gas hydrate reservoirs.